The present invention relates to the field of food packaging, and particularly to the preparation of sealed containers of mixed or heterogeneous food products.
In general, when food products, other than staples and dried foods, are to be packaged for long term storage, they are placed in sealed containers such as cans, sealed foil trays or pouches, or multi-layer paper/polymer/foil packages. These are sealed against the atmosphere and may additionally provide a relatively strong structure (in the case of canned goods) suitable for handling and storage at room temperature, for example, on shelves or bins for extended periods of time, or suitable for cold storage. Such sealed containers must be sterile, and current industry practice, particularly in the United States, involves heat sterilization.
The level of applied heat, that is the pressure, temperature, heating medium and duration of heating, may vary depending on the conditions under which processing or cooking of the ingredients, the filling of the packages and the sealing operation have been carried out. For canned goods, post-sealing retorting of the cans is commonly employed. This involves maintaining the entire sealed can at a temperature above a specified sterilizing temperature for a time sufficient to heat the can and every portion of its contents to the sterilizing temperature. Typically the processing or retort temperature is substantially above normal boiling temperature, and the process may be carried out at elevated pressure to prevent rupture or ballooning of the container. Similar sterilization processing is used for foil-sealed freezer products. Certain earlier stages of food processing also employ elevated pressure and temperature, where the pressure elevation serves the further advantage of preventing evaporative cooling or moisture loss during the heating involved in such cooking, sealing or packaging phases. By way of example, U.S. Pat. No. 5,422,130 illustrates a process wherein a packaging apparatus maintains an elevated pressure to minimize evaporation, and various load locks are used to provide a stepped cool-down and pressure reduction cycle for relieving packaging stresses.
Retorting is cheap and effective. This makes it especially suited to process lines wherein the earlier stages of cooking and assembling the product are carried out under non-aseptic conditions. Non-aseptic processing followed by packaging and retorting allows normal factory assembly lines with human operators to conveniently carry out tasks required for cooking, assembling and filling products such as packaged meals, where the assembly may involve steps such as trimming or arranging components of the meal in positions on a tray, and performing decorating steps or checking their quality before the package is sealed. However, in these cases where the food product is assembled from several components at cooler temperatures, the entire unit must be sterilized, and required sterilization time for the entire packaged product may be quite long. The quality of the various cooked, parboiled, simmered or otherwise fully or partially processed components of the product may deteriorate upon exposure to the high sterilization temperatures when these are maintained for such lengthy sterilization times. Indeed, the stringent conditions of retort sterilization alone may overcook a number of component ingredients. This is also a problem for the basic processing of food products involving large solids, which require lengthy heating to attain a sterilization temperature. Lengthy heating also limits the types and materials of packaging that may be used.
When cost is not a driving consideration, it is possible to address these concerns, for example, by providing a final filling line in a high pressure environment, in which the human operators enter a high pressure chamber where food product components may be maintained at a high temperature without undergoing evaporative cooling, and the operators may then perform all preparation and assembly tasks up to the filling and sealing steps while the ingredients are maintained above a threshold level at which resterilization does not become necessary. In this case, the packaged goods may require only a brief heated holding cycle, or a shorter time retort to achieve sterility, rather than reheating the entire contents of the packages.
However, such elaborate pressurized processing facilities can only be justified in the case of a few high-priced products such as luxury frozen meals. The vast majority of packaged foods involve more mundane products, such as stews containing heterogeneous size chunks of meat or potato, products involving pieces of one or more fruits or vegetables of differing but relatively large size, and other materials which either because of their size, or because they include a fragile or heat sensitive product component, render it difficult to arrange for cooking, filling and for sterilization regimes that do not degrade or interfere with one or more of the solids or other components such as sauces, vegetables or toppings that make up the packaged food product. Even for some simple single-ingredient or substantially homogeneous products, like canned peas, the basic retorting cycle may exceed the required cooking cycle, or may result in a product which is necessarily overcooked, or is mushy, or else requires compensatory use of under-ripe starting produce or addition of flavor-enhanced liquid fractions. A basic problem in the preparation of such products is that the cumulative heating involved in all stages of processing degrades the quality of one or more components of the product.
Accordingly, it would be desirable to provide an enhanced food packaging system that achieves sterilization without impairing food texture or taste.
It would further be desirable to provide a food packaging system capable of fast sterilization.
It would also be desirable to provide a packaging system in a process line that coordinates processing, filling, sealing and sterilization to produce sterile, storable packages of tasty food.